(1) Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device for compressing picture signal.
(2) Description of the Related Art
In recent years, an increasing number of video recorders which record and reproduce audio and video signals with the use of a DVD (Digital Versatile Disk) or HDD (Hard Disk Drive) are put on the market.
Generally, as an information compression scheme used in recording signals on such recording media, MPEG (Moving Picture Coding Experts Group)-2 Video format is used for video signal, and MPEG1 Layer 1 or 2 or the like is used for audio signal.
To store the signals compressed by such methods on a recording medium, both of AV (Audio and Video) signals, including synchronizing signal, need to be further combined into one and then be multiplexed into data in a format suited for the physical format, protocol, etc. peculiar to DVD or HDD. As such format, MPEG2 PS (Program Stream) or TS (Transport Stream) is generally used.
Recently, one-chip LSIs (Large Scale Integrated Circuits) capable of compressing and multiplexing AV signals have come onto the market. In the present specification, this type of LSI is called MPEG2 encoder.
Meanwhile, with the commercialization of video recorders using DVD or HDD as a recording medium, a need has arisen to protect contents against illegal copying etc., and a technique of inserting a copy protection signal in video signals is used as one of measures to meet the need.
Specifically, a signal indicating “copy permitted”, “one copy permitted” or “copy not permitted” is inserted in a VBI (Vertical Blanking Interval) of every field of video signal, and a video recorder looks up such signals to restrict copying.
FIG. 12 illustrates an exemplary configuration of a conventional video decoder using an HDD as a recording medium.
In the figure, an NTSC (National TV Standards Committee) decoder 10 converts a video signal into a digital signal and outputs the converted signal.
A VBI detecting section 11 detects protection information inserted in the VBI of the NTSC signal and notifies a CPU 19 of the information via a bus 22.
An audio A/D (Analog to Digital) converter 12 converts an audio signal into a digital signal.
An MPEG2 encoder 13 compresses the digitized NTSC signal (hereinafter called video data) and the digitized audio signal (hereinafter called audio data) according to MPEG2 format, and outputs the result.
An IDE (Integrated Drive Electronics) I/F (Interface) 14 controls an HDD 15.
Under the control of the IDE I/F 14, the HDD 15 records the data supplied from the MPEG2 encoder 13 into a predetermined region thereof, and also reads out the data recorded in the predetermined region to be supplied to an MPEG2 decoder 16.
The MPEG2 decoder 16 decodes the data compressed according to MPEG2 format, and outputs the video data and the audio data.
A video AMP 17 converts the video data to analog NTSC video signal, and outputs the converted signal.
An audio D/A (Digital to Analog) converter 18 converts the audio data to analog signal and outputs the result.
The CPU (Central Processing Unit) 19 controls the individual parts of the device and performs various operations in accordance with programs stored in a flash ROM (Read Only Memory) 20.
The flash ROM 20 stores programs to be executed by the CPU 19 and various other data.
An SDRAM (Synchronous Dynamic Random Access Memory) 21 temporarily stores programs being executed by the CPU 19 as well as data derived in the middle of operations.
The bus 22 interconnects the VBI detecting section 11, MPEG2 encoder 13, IDE I/F 14, MPEG2 decoder 16, CPU 19, flash ROM 20 and SDRAM 21, and permits exchange of data between these elements.
Operation of the conventional device will be now described.
Video and audio signals are input to the NTSC decoder 10 and the audio A/D converter 12, respectively, whereupon the NTSC decoder 10 converts the video signal to digital signal in compliance with an encode request from the CPU 19 and outputs the converted signal, and the audio A/D converter 12 converts the audio signal to digital signal and outputs the result.
The VBI detecting section 11 detects the protection information inserted in the VBI included in each field of the video data output from the NTSC decoder 10, and supplies the detected information to the CPU 19 via the bus 22. The protection information indicates, for example, “copy permitted” or “one copy permitted” or “copy not permitted”, and based on the information the CPU 19 determines whether copying is permitted or not.
On detecting “copy permitted”, the CPU 19 instructs the MPEG2 encoder 13 to start encoding. As a result, the MPEG2 encoder 13 compresses the video data supplied from the NTSC decoder 10 and the audio data output from the audio A/D converter 12, according to the MPEG2 scheme, and outputs the obtained data.
The CPU 19 instructs the IDE I/F 14 to store the data output from the MPEG2 encoder 13 in a predetermined region of the HDD 15. Operation like this is continued until the input of video and audio signals ends.
Reproduction of data stored in the HDD 15 will be now described.
The CPU 19 instructs the IDE I/F 14 to reproduce certain data, whereupon the IDE I/F 14 reads out corresponding data stored in a predetermined region of the HDD 15 and supplies the data to the MPEG2 decoder 16 via the bus 22.
The MPEG2 decoder 16 decodes the data supplied from the IDE I/F 14, and supplies the obtained video and audio data to the video AMP 17 and the audio D/A converter 18, respectively.
The video AMP 17 converts the video data supplied from the MPEG2 decoder 16 into analog signal and outputs the result. The audio D/A converter 18 converts the audio data supplied from the MPEG2 decoder 16 into analog signal and outputs the result.
When the information inserted in the VBI is reproduced, the obtained information sometimes includes noise superimposed thereon, and in such cases, the copy protection signal can be erroneously detected.
To prevent such erroneous detection, when an identical signal is detected consecutively a predetermined number of times (e.g., ten times), for example, the detected signal may be judged valid and the specified operation may be executed, whereby the probability of erroneous operation can be lessened.
However, to carry out such control, while the protection information is detected consecutively the predetermined number of times, the MPEG2 encoder 13 needs to be operated to store the generated data in the HDD 15, and when an identical protection signal is detected the predetermined number of times and thus a requested operation is established, the requested operation is executed. Accordingly, even in the case where the requested operation signifies “copy not permitted”, data is stored in the HDD 15.
To solve the problem, data that has been stored in the HDD 15 may be deleted afterward. However, once data is compressed by the MPEG2 encoder 13, the correspondence of the compressed data to video data before the compression is not clear. Thus, since it is not clear from which location to which location of data in the HDD 15 should be deleted, it is difficult to delete the compressed data afterward.